Nesa strips



Aug. 1l, 1959 M. v. KALFAIAN 2,899,488

COLOR IMAGE AND FLYING SPOT SCANNER CONTROL OF DUAL` PHOTOCONDUCTIVE FILM Filed March 17, 1955 DUCTIVE FILM OSA/C C'UNDII 1'0R E L EME N T5 PHOTOCl/NDUC TVE FILM PHOTOCO RH@ 8*63 ww ngz ` ELlaHr-.souncs A INTERR UPTION WAVE INVENTOR.

mz l *4* P @g3 .tia'l across this impedance.

COLOR IMAGE AND FLYING SPOT SCANNER gglITROL F DUAL PHOTOCONDUCTIVE Meguer V. Kalfaian, Los Angeles, Calif.

v Application March 17, 1955, Serial No. 494,940

4 Claims. (Cl. 178-5.4)

This invention relates to color television, and more particularly to the camera,. or to the pick-up color screen and lassociated equipment, of a color television system. The main object of this invention is to provide a light sensitive composite screen, which is capable of translating a primary optical image into a series of electrical output signals representative of primary color component'areas of 'the image by the aid of a scanning beam of light.

2,899,488 Patented Aug. 1l, 1959 ICC when the path between electrodes 2 and 5 is closed by a direct current potential source 7 in series with an limpedance 8, the instantaneous current flow through the impedance 8 will Ythen represent the amount of admittance between photoconductive layers 1 and 3 at the instantaneous position of the beam of light falling upon photoconductive layer 5. f

As is common characteristics with photoconductive image screens, a storage of change in resistivity is effected,

l either by the optical image falling upon it, or, by the Another object of this invention is to provide a single light y' sensitive screen selectively responsive'to each'primary color of the image to be televised. A corollary object is to provide a single composite color image pick-up screen, which is capable of translating a televised color image into a simultaneous additive system. A further object of this invention is to provide a composite colorimage pickup screen, which is capable of operating with or without vacuum enclosure.

Among various forms of monochrome television pickup screens, photoconductive screens have been utilized in practice, making use of their characteristic changes in cross-sectional resistivity under radiation of light in varying intensity. These photoconductor screens, or films, which may be in the order of 5 microns thick, so as to avoid transverse distribution of the cross-sectional admittance changes, may comprise, for example, layers of antimony trisulde evaporated over a substrate consisting of light transparent conductive glass. When an optical image is projected upon this photoconductive film, through the conductive glass, its cross-sectional admittance variations may be explored elementally by. a scan- -ning electron beam, in 'vacuum enclosure, for the production of output video signals. The functional mechanism is that, as the beam scans an illuminated area of the photoconductive film, the admittance imposed upon this varea causes beam current to pass onto the glas's .conductor lm and return to the emitting cathode through a suitable impedance, for developing a representative poten- Whereas, when the electron beam travels across a dark area of the photoconductive iilm, the admittance at this area being extremely low, as compared with the illuminated area, the beam current is accordingly prevented from passing on to the Yglass conductor lm, with consequent quiescence in the output impedance.

Instead of utilizing an electron beam for the scansion of an illuminated photoconductive film, it is possible to effect similar scansion by a scanning beam of light proiected upon an auxiliary photoconductive film, acting as an on-and-off gating medium for the transfer of energy of the signal producing photoconductive iilm in a closed electrical circuit. To illustrate how this particular action may be achieved, assume, in reference to Fig. l, that'the signal-producing photoconductive iilm 1 receives the optiical limage through the 'light transparent conductor screen 2, and the auxiliary photoconductive lm 3 receives the V*illumination Yof the scanning beam of light from source 4, through an auxiliary light transparent conductor screen 5.' The intensity of the scanning beam of light is made scanning beam of light, as utilized in the embodiment of this invention. Although this storage may be erased during a frame period, ,the output video signals produced across impedance 8 might be considered to be cumulative, since the instantaneous current iiowing through electrodes 2 Vand 5, representative of the illumination of any successive elemental image could include the additive illumination of a preceding elemental image. Whilefaithful video signals maybe derived from this type of output signal formation, by modified circuit arrangementajt might be simpler, and preferable, to translate this type of signal into pulses at the rate of the highest frequency that is necessary in forming the television image. Inv one simpler form, the scanning beam of light may be interrupted, for example, by interruption wave source in block 9, at the highest frequency rate that is necessary in forming the televised image. Then, by placing a small coupling capacitor 10 at the output of impedance 8, the resultant waveform of the output video signals will be in pulses, the pulsations of which may either be filtered out, or utilized as they are, in the final modulation of the transmitting equipment associated therewith.

, A color imaging process may be considered as a multiple action of the monochrome imaging process. For example, in monochrome television imaging process, a complete picture frame is divided into a plurality of minuteindividual image elements. When it is desired to develop these elemental images in primary color component elements, for example, in rst, second and third primary colors, sequentially or simultaneously, it is only necessary to subdivide the area of each image Velement into -rst, second and third primary color sub-areas, the magnitudes of the color component elements containingin these sub-areas being dependent upon the composite lhue formation of the image elements. Thus, in one simple Iway of achieving this multiple imaging process, the translucent electrode 2, in Fig. 1, may be divided into a plurality of spaced parallel strip-like conductor electrodes, interleaved into iirst, second and third sections, and electrically connected to the translucent electrode 5, in series with potential supply 7, and in series with first, second and third impedances; these replacing the impedance 8. By disposing a preassigned color iilteringrlm, havingjthe proper sub-division of color component areas, adjacent to ythe translucent (sub-divided) electrode 2, the required color imaging process may then be effected.

Further details of a complete color televisionrpick-up system will now be given in the following specification, in conjunction with detailed drawings, wherein: Fig.l 1 represents the basic arrangement of a monochrome image Y pick-up system; Fig. 2 is a modication of Fig. l, for

coupling capacitor C3.

Referring tothe illustration ofi Fig. V2, the composite image pickup screen, in.r sirrniltaneous primary colors',-.

elassertrenspar @plastieplafe serviaaas the base plate of they cornnosite layers 0f the srserl- @ver this .lishstransnarst' plate itt, which may be. f

transparent plate there is `slated @901er @lter @liu 12, f

which comprises a large number kci sequentially amused lprimary#colori lter stripes, 'for example, the colors Qi creen (Gl, redCR) and blue (B), extending transversely thereacross; O ver .this color filtering film is disposed plurality of translucent conductor strips 13,-adjacently aligned with the lter stripes of color iilrn 12. Dyer.-

lying this screenf of conductorfstrips is a photoconductiye llayer 14.which lrnayconsist, of example, o fantimony trisulhde, amorphous selenium, or others, as foundsuit- `able for the particular purpose.. The next lamina con,- siststii an opaque mosaic pattern of mutually insulated conductor layer 1'4"; connective f mosaic elena-:nts 15;

photoconductor layer 16; translucent conductor electrode 17; through battery 23; and through resistors R1 to R3, independently, proportionally .corresponding to the resistivity of photoconductor layer 14 .at any given elemental Aimage area, as scanned by 'the beamof lightupon the adjacently positioned-photoconductor. layer 16. Inorder Y tofpbtain simultaneous primary color video signals', repl' resentative of-each image element, the conductive'` strips 13 are made very'narrow in width, so thaty at least three strips, comprising the three primary color output signal plates, intercept the projected beam area. Accordingly,

as the beam of` light forms a scanning raster uponl the -photoconductive layer16, the output video image elements are produced in simultaneous .primary color cornponent signals across the preassigned resistors R1. to R3.

The photoccmductiveA layer is very thin in comparison. to

minute ctmductorv `elements 15, closely 'inl contaetwith' the photoconductive layer 14.' Over'thismosaic of con ducti've elements vthere is placed another layer of photoconductive lamina `16, closely in electrical 'contact with lthe mosaic elements 15, whereby these minute conducttve elements serve to provide individual. fore-and-aft "electrical pathsbetween; the photoconductor layers 14 l land-16, whileV at the same time preventing transverse electrical paths due` to their individual insulations one -'fr ;m:l another.v .Finally overlying the photoconductor v lamina 16 'is a uniform translucent conductor electrode -1', throughwhich `as'canning beam of light is'projected fupbn the surface of the photoconductor layer 16. This beam. of light is produced upon the phosphor screen 1S of an yordinary projection type-of cathode raytube 19,

nals from generator block 22. In its final arrangement,

las illustrated, the conductor strips 13 are divided into rst, second and third interleaved sections, in` alignment wi'ththe adjacently disposed green, red and blue color filtering `stripes of film 12, respectively, and these three sections are independently terminated to the conductor electrode 17 through resistors R1, R2 and R3. As shown in the arrangement, the video voltage developed across resistor R1 represents the green primary color -video signal, connected to an outgoing circuit through a small coupling capacitor C1; the video voltage developed across resistor R2 represents the red primary color video signal,-

connected to an outgoing circuit through a small coupling capacitor C2; and the' video voltage developed facross resistor R3 represents the blue primary color video signal, connected' to an outgoing circuit through a small l A conventional optical system, not shown, may be used to focus upon the image pick-up screen an optical image of whatever scene is to be televised. The. light forming this image passes through glass plate 1'1; striped color iilrn 12; and translucent conductor strips Y13 into photoconductive layer 14. From point to point within layer 14, its electrical conductivity varies according to the intensity of illumination received. Any current'flow between the conductor strips 13 and electrode 17 is normally prevented by the normally high dark resistance of photoconductor llayer 16; as the mosaic screen 15 is made completely opaque to light, and the light received by photoconductive layer 14 cannot pass on to the photoconductor 16. As the beam of light, arriving from monotone raster 18, through translucent conductor elecufrode 17,V scans the photoconductive layerl, the resistivity of this layer is lowered in elementalI progression, and current ows between the conductor strips 13; photothe `width of. a conductor strip, `so .that itsresistance to transverse currentsis much'rhigher than itfsresistanceto foreand-.aft currents, and transversecurrents are negli? sible-V Presently available photoconductive-materials lhave riser and decay time constants, in resistivity changes, much slower than desired for the arrangement given inFig. 2.

This tends, first, to c lecreasey the utilization of the onaruil o ff gating action ofA the photoconductive layer 16,

and serene. te, form `sumulative Output Avideossnals,

:which vmilstfbr madisd- This modification. may be k1 -ate necessary for picture conveyance. Then, by

use ef Small Qapacitanes .for 01.1.2.2` and. Cythe` slow? achieved easily, in one form of operation, by interrupting the scanning beam of' light at the maximum frequency I' variations of cumulative currents through resistancesRl t0 R3- wiltbe cancelled eut and onlyk signalpulsswill appearatthe outputs 0f, these coupling capacitors The phosphor Screen 18' et projection type of cathode ray tube 19 ,isureferablviof short persistancetype, which is presently available, as utilized in flying spot iilrn scanner cathode rayitubes. .The beam interruption wave, as generated in hlocls'24, may be either sine wave, or abruptly changing pulses. And finally, the scanning wave generator, as represented by block 22, may be conventional, theoutput wave currents of which are applied to conventional` beam deecting yoke 2 1, for the required scansion. A

In an image reproducing system of high image resolution, the `number of interleaved conductor strips 1 3 should `be substantially high. This means that the inherent capacitances between` adjacent strips will consequently be high, as they will necessarily be in close proximity; especially when the number of strips isso high that more than one strip` intercept the beam simultaneously. This tends .tol cause cross rel between the signals representing different colors, and accordingly, special compensating arrangement is utilized. in the form as shown in Fig. 3. The resistors R4, RS-and R6 represent the resistors R1 to- R3, respectively, the` output voltages across which drive` thelcontrol grids of cathode `follower and phase inverter tubesVh toHV3, respectively. Thefphase inverted potentials across plate circuit resistors R7 to R9 arethen intercoupledwith the grid circuits `of these tubes, by neutralizing capacitors 25, 26, 27 and 28, the values of whichare adjustedequal to the inherent capactive intercouplings between the conductor strips 153,

wherebyeffecting substantially complete cancellation of these inherent capaci-tive intercouplings. The output video signals are then `taken `from` the cathode circuit resistors The translucent-conductor electrodes 13 and 17 may be made byA a thin layer of metal vaporization, for example, few riufcro'nsl thick; These electrodes may also `be made o f'f conductive g1ass,.which may be formed, for example,by exposing thcscreenjin heated conditionto the vapors of silicon, or titanium ch10rides and af terwards placing in a slightly reducing atmosphere. The

continuous transparent conduct-ing lilm produced by this process may then be machined, or by other suitable means, to form the mutually insulated conductor strips 13. Other processes of forming the translucent strips 13 may also be utilized, for example, as disclosed in copending application by R. E. McCoy and myself, Serial Number 277,632, March 20, 1952, for Color Television Cameras.

It may be included herein that the purpose of arranging the image pick-up screen without vacuum enclosure is to render it independent of vacuum tube replacement. However, the screen may be enclosed in the vacuum cathode ray tube 19, in which case, the phosphor screen 118 may be coated upon the surface of translucent electrode '17, and luminesced by the scanning beam 20 produced in the vacuum envelope. This phosphor screen may either be coated facing the electron beam, for eX- citation by low velocity beam, or, facing the photoconductor layer 16 for excitation by high Velocity beam, for greater amount of light excitation upon the photoconductive layer 16.

While the present invention has been described in reference to color image pick-up devices, it shouldbe understood thart the system is basically a monochrome image pick-up, for example, by connecting all the conductor strips 13 in parallel, or originally forming a uniform conductor surface, and utilizing a single output impedance lfor delivering monochrome video signals. Since the system of color image pick-up is a multiple process of the monochrome image pick-up, it is accordingly to be understood that the system of monochrome image pick-up is to be represented herein as the preferred embodiment of the invention, and the steps in which these images may be translated into different separate primary color component parts are rto be modifications thereof. The appended claims will, accordingly, cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim, is:

1. An optical composite screen, which comprises a rst photoconductive surface adapted to translate optical images into representative electrical resistivity changes; a iirst translucent electrode, spaced coextensive and in close proximity with said surface; a mosaic of mutually insulated conductive elements in close contact with the first photoconductivity surface, remote from said electrode; a second photoconductive surface adapted to translate optical images into representative electrical resistivity changes, spaced coextensive and in close proximity with said mosaic elements; and a second translucent electrode spaced coextensive and in close proximity with the second surface, remote from said mosaic, whereby forming a mosaic of independent resistivity paths between the rst and second electrodes, corresponding rto representative values of optical images falling simultaneously upon said iirst and second photoconductive surfaces through said translucent electrodes.

2. The composite screen as set forth in claim 1, wherein, said rst electrode comprises plurality of strip-like translucent electrodes divided into rst, second and third sections, said sections interleaved into repeating groups of first, second and third strips, respectively; and including a color filtering surface arranged into plurality of strips in repeating groups of irst, second and third primary colors optically aligned with said first, second and third strips, respectively, whereby said mosaic of resistive paths identifying .the primary color components of the optical image falling upon said iirst photoconductive surface within the areas of said strip-like sections.

3. The composite screen as set forth in claim 1, wherein is included means for projecting an optical image upon said iirst photoconductive surface through said first translucent electrode; means for producing a beam of light in constant intensity; means for projecting and forming a scanning raster upon said second photoconductive surface by said beam through said second electrode, whereby completing elemental resistive paths between said rst and second electrodes, representative of elemental areas of said projected optical image; and a series-connected impedance means and a potential source connected electrically between said first and second electrodes, thereby causing electric current to pass through the impedance means proportionally corresponding to sa-id elemental changes of resistivity between the first and second electrodes.

4. Ihe composite screen as set yforth in claim l, wherein is included means for projecting an optical image upon said rst photoconductive surface through said iirst translucent electrode; means for producing a beam of light in constant intensity; means for projecting and forming a scanning raster upon said second photoconductive surface by said beam through said second electrode, whereby completing elemental resistive paths between said iirst and second electrodes, representative of elemental areas of said projected optical image; a seriesconnected impedance means and a potential source connected electrically between said first and second electrodes, whereby causing electric currents to pass through fthe impedance means proportionally corresponding to said elemental changes of resistivity between the rst and second electrodes; means for interrupting said projected beam at a predetermined high frequency rate, whereby distinguishing the currents passing through said impedance means between retention currents, as caused by sluggish operating characteristics of some photoconductive elements, and image-signal currents; and means for filtering out said retention currents, whereby only said interrupted currents are derived as representative of said image signals.

References Cited in the iile of this patent UNITED STATES PATENTS 2,150,168 Ives Mar. 14, 1939 2,177,736 Miller Oct. 31, 1939 2,288,402 Iams June 30, 1942. 2,618,761 Rose Nov. 18, 1952 2,689,270 Weimer Sept. 14, 1954 2,734,938 Goodale Feb. 14, 1956 

